Belemnoid Arm Hooks from the Middle–Upper Albian Boundary Interval: Taxonomy and Palaeoecological Signiﬁcance

Home , Belemnitina, Dipoloceras, Hibolites, Phragmoteuthida

Pala¨ontol Z (2011) 85:287–302 DOI 10.1007/s12542-010-0092-7

RESEARCH PAPER

Belemnoid arm hooks from the Middle–Upper Albian boundary interval: taxonomy and palaeoecological signiﬁcance

Jens Lehmann • Alexandra Solarczyk • Oliver Friedrich

Received: 9 July 2010 / Accepted: 15 December 2010 / Published online: 11 January 2011 Ó Springer-Verlag 2011

Abstract For the first time, a large number of belemnite The shift in belemnite abundance might be interpreted as arm hooks is described from the Lower Cretaceous triggered by a combination of warming and increased (Middle–Upper Albian boundary interval) of the classic productivity and/or condensation. locality of Folkestone in southern England. The arm hooks originate from six individual claystone layers; Keywords Belemnites Arm hooks Palaeotemperature some could have been attributed to the parataxon Arites Palaeoproductivity Cretaceous Albian England sp. Comparison is made with material from a drill core from Hannover, northern Germany that shows similarities Kurzfassung Erstmals wird eine gro¨ßere Anzahl von and also allows the description of a new parataxon: Belemniten-Armhaken aus der Unterkreide (Grenzbe- Hughowenites incurvatus n. gen. n. sp. The belemnite reich mittleres/oberes Alb) der klassischen Lokalita¨t hooks might belong to either the diplobelids Conoteuthis Folkestone in Su¨dengland beschrieben. Die Armhaken and Pavloviteuthis, both characterised by a reduced guard stammen aus sechs verschiedenen Tonsteinhorizonten, and thus very rare finds at Folkestone, or the abundant einige ko¨nnen dem Parataxon Arites sp. zugeordnet guard-bearing belemnitinid Neohibolites.Withinthe werden. Ein Vergleich mit Material aus einer Bohrung studied succession, belemnite hooks are more abundant in in Hannover, Norddeutschland, zeigt U¨ bereinstimmun- sediments deposited during an earliest Late Albian gen und fu¨hrt zudem zu der Beschreibung eines neuen warming event that is accompanied by an increased Parataxons: Hughowenites incurvatus n. gen. n. sp. Die abundance of guards of the belemnite Neohibolites. Belemnitenhaken du¨rften entweder von den Diplobe- Concurrently with this warming event primary produc- liden Conoteuthis und Pavloviteuthis stammen, die durch tivity was enhanced, as indicated by fluctuations in the ein reduziertes Rostrum charakterisiert sind und deren composition of the calcareous nannoplankton assemblage. Rostren deshalb in Folkestone sehr selten sind, oder dem sehr haüfig auftretenden Rostrum-tragenden Be- lemnitiden Neohibolites. Innerhalb des untersuchten Profils sind Belemnitenhaken in Sedimenten, die wa¨h- rend eines Erwa¨rmungsereignisses im fru¨hen Oberalb J. Lehmann (&) A. Solarczyk abgelagert wurden am haüfigsten, ein Zeitabschnitt der Fachbereich Geowissenschaften, Universita¨t Bremen, zudem durch das haüfigere Auftreten von Belem- Klagenfurter Strasse, 28359 Bremen, Germany e-mail: [email protected] nitenrostren von Neohibolites charakterisiert wird. Parallel zur Erwa¨rmung war die Prima¨rproduktion er- A. Solarczyk e-mail: [email protected] ho¨ht, wie durch Haüfigkeitsfluktuationen in den Verge- sellschaftungen indikativer kalkiger Nannoplanktonarten O. Friedrich belegt ist. Das vermehrte Auftreten von Belemniten Institut fu¨r Geowissenschaften, Facheinheit Palaöntologie, ko¨nnte durch eine Kombination von Erwa¨rmung und Goethe-Universita¨t Frankfurt, Altenho¨ferallee 1, 60438 Frankfurt/Main, Germany erho¨hter Produktivita¨t und/oder Kondensation erkla¨rt e-mail: [email protected] werden. 123 288 J. Lehmann et al.

Schlu¨sselwo¨rter Belemniten Armhaken (Sellwood et al. 1994; Ditchfield et al. 1994; Pierri et al. Palaötemperatur Palaöproduktivita¨t Kreide Alb 1995; Price 1998), because belemnites are composed of England low-Mg calcite and thus the chance of preserving the ori- ginal carbonate is high (e.g. Marshall 1992). Belemnite values are nevertheless different from values obtained from Introduction other groups of organisms, and reasons for this remain unclear (Price 1998; Voigt et al. 2003). As an example, After the pioneering work of Neumayr (1883), who measurements obtained from the Late Cenomanian Actino- established faunal provinces and was among the first to link camax plenus indicate a cooler temperature compared with macrofossil distribution to climatic differences, it soon those from brachiopod shells from the same region or results became clear that many groups of Jurassic and Cretaceous obtained from modelling (Voigt et al. 2003). Hence, pal- belemnites show differing palaeogeographic distribution aeoceanographic interpretation is not unequivocal, and in patterns. In fact, belemnite faunas typifying the Boreal- this instance Voigt et al. (2003) propose either migration Arctic region can be distinguished from those characteri- from a cooler/deeper water mass or an unknown vital effect. sing the Tethyan region (e.g. Stevens 1963; Combe´morel Nevertheless, geochemical data derived from belemnite et al. 1981; Mutterlose 1986; Doyle 1992; Gale and rostra constitute important data for the palaeoclimatologic Christensen 1996; Alsen and Mutterlose 2009; Wilmsen interpretation of belemnites. et al. 2010). Several decades ago it became clear that These different approaches show that belemnite data are generalisations about the palaeotemperature preferences of useful for reconstructing palaeoclimates with respect to belemnite higher taxa are not possible (e.g. Stevens 1965). palaeoceanography. However, the classical approach in Different belemnite families and genera show different directly relating the distribution of belemnite guards to temperature tolerances, while the temperature preference climatic factors is naturally limited in its argumentation, of some belemnite groups changed during their evolution. and a number of contradictions still cannot be explained The Tethyan belemnopseid Hibolites, for example, is (e.g. Doyle and Pirrie 1999). Therefore, further environmental regarded as ancestral to the important Boreal family Be- factors have been considered to avoid the over-simplification lemnitellidae as well as the southern endemic stock of the that water temperature had the major biogeographical control Dimitobelidae (Doyle 1987a; Doyle 1987b; Christensen on distribution patterns. These factors include changing 1988), therefore indicating a significant evolutionary oceanography and physical barriers, water depth and salinity change in temperature sensitivity. Changing palaeotem- (Doyle 1988). Here, we test these different hypotheses by perature tolerance can also be traced at lower taxonomic investigating the immediate response of belemnites to a dis- levels, as in the case of the widespread Aptian-Albian crete, short-term climatic warming event that is known from a emigration from the Tethys by the belemnopseid Neohib- number of further proxies besides the belemnite data them- olites (Doyle 1987b). Based on palaeobiogeographical selves. We use belemnite hooks obtained from washed clay- patterns, Mutterlose et al. (1983) were able to distinguish stone samples for this innovative approach. between eurythermal and stenothermal belemnite genera in the Early Cretaceous. Hibolites and Neohibolites are eurythermal warm-water genera with high potential for Locality details and methods thermal adaption that occurred in the Boreal as well as in the Tethys, whereas Duvalia, Berriasibelus and Parahib- The present paper deals mainly with a series of samples olites, among others, are stenothermal warm-water genera from the classical section near Folkestone, southeastern that are limited to the Tethyan realm (Mutterlose et al. England, that is located in the Anglo-Paris Basin (Fig. 1). 1983). Additionally, test samples and single specimens originating Use of carbonate oxygen isotope ratios in belemnite from the Hannover area in northwestern Germany (Lower guards for estimating palaeotemperatures sheds new light Saxony Basin) have been considered, a region that showed on belemnite palaeoecology and allows their application as an open shelf connection to the Anglo-Paris Basin (Fig. 1). palaeoclimatological and palaeoceanographical proxies (e.g. Bodylevskii 1957; Tejs and Naidin 1969; Wefer and Folkestone section Berger 1991; Price 1998). In the early years of isotope analysis, belemnite rostra were regarded as imperfect Important accounts of the research history of the classical sources for deriving palaeotemperature estimates, since it Gault Clay section (Middle–Upper Albian) at Copt Point, was thought that there might be a high ratio of secondary East Cliff, Folkestone have been provided by early authors cement, leading to alteration of the primary signal (e.g. such as Parkinson (1819), Fitton (1836), De Rance (1868) Wefer 1982). These doubts largely have proved unfounded and Price (1874) and, more recently, by Casey (1966) and 123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 289

Fig. 1 Palaeogeography of the early Late Albian in northern Europe with localities and areas mentioned in the text. Localities: Fs Folkestone, Kent; As Ashford, Kent; HL drilling core in Hannover-Lahe, Lower Saxony; Ah O¨ lbach stream cut S of Ahaus, Northrhine- Westphalia. APB Anglo-Paris Basin, LSB Lower Saxony Basin. Map modiﬁed after Ziegler (1982, 1990)

Owen (1971a, b). In particular the outstanding preservation point in the cliff at 51° 502.6200N, 01°11057.9500E was recorded of ammonites, including their iridescent shells, is famous using GPS and is documented in Fig. 2. Each sample was and constitutes a major reason why this site has been—and obtained over a sediment thickness of *0.5 m (Fig. 3). First, still is—intensively collected (Clouter 2007). The dried and weighed samples of between 2,066 and 3,909 g were ammonite fauna was monographed by Spath (1923–1943), carefully mechanically disaggregated and then washed and and the biostratigraphy has been revised, for example, by sieved over a 63 lmmesh(Table 1). For a detailed description Owen (1971b, 1976). Results of more recent investigations of this method see Wissing and Herrig (1999). Samples were on calcareous nannoplankton (Kanungo et al. 2004; dry-sieved into[63 lm,[125 lmand[250 lm fractions. All Kanungo 2005) and dinoflagellate assemblages (Dunn et al. fractions were picked completely, and a total of 161 belemnite 2006) have not yet been fully published. The belemnite hooks were obtained from the 63–125 lm fraction, 19 hooks Neohibolites minimus (Miller ex Lister, 1826) occurs fre- from the 125–250 lm fraction and no hooks from the[250 lm quently in the Middle–Upper Albian at Folkestone (see fraction. Since the dry weight of samples differed, we norma- Swinnerton 1955 and Clouter 2007). Recently, Knight lised values to equal weight of 500 g to compare the results. We (2010) figured a well-preserved specimen with phragmo- used the formula (n/w) 9 500 (here called the hook abundance cone and aragonitic pro-ostracum preserved in association index), with n being the total number of hooks per sample, w the with the rostrum. Oxygen isotopes from belemnite guards total dry weight, and 500 the factor to calculate the hook from Folkestone were used by Bowen (1961) for palaeo- number per 500 g (Fig. 3,Table 1). The hook abundance index temperature estimates, and Spaeth (1971b) demonstrated shows values around 3.5 for samples 1–2 and 5–6 but increases that they are very well preserved. Additionally, a couple of significantly (up to 5.7) in samples 3 and 4. phragmocones referred to diplobelid belemnoids have been Scanning electron microscope images (Plate 1) were recorded from the Albian of Folkestone: Conoteuthis taken using a Zeiss Supra 40 SEM at the Faculty of Geo- woodwardi Spath 1939 and Pavloviteuthis cantiana (Spath sciences, Bremen. The terminology of hook features as 1939) (Woodward 1856; Spath 1939; Jeletzky 1981; not defined in Fig. 4 follows Kulicki and Szaniawski (1972), V. vectensis Spath 1939 as stated by Fuchs et al. 2004, Fuchs (2006) and others. which originates from the Aptian). Sampling took place in July 2008 (J.L., O.F.). O¨ lbach section Our study was systematically performed on six samples from six individual beds of the Folkestone section obtained The Middle–Upper Albian O¨ lbach stream-cut near Ahaus, during fieldwork in July 2008 (J.L., O.F.). Our sampling northwestern Germany was mentioned by Bentz (1930) and

123 290 J. Lehmann et al.

Fig. 2 The Gault Clay (Lower Cretaceous, Albian) section at Copt bed of the Middle Albian [boundary between beds III and IV sensu Point, Folkestone. a Sampling points at 51°502.6200N, 01°11057.9500E Price (1874)]. b Panoramic view, the rectangle shows the position of in the upper center of the picture: 1 indicates the lowermost sample the close-up of the sampling points in a and 6 the uppermost (compare Fig. 3). The sulphur band is an index brieﬂy described by Kemper (1976), who also ﬁgured some claystone material with total weight of 5,000 g that was fossils. Owen (1979) referred to the ammonite fauna. This carefully mechanically disaggregated, dried, then washed locality exposes the Minimus Greensand that is named and sieved following the same procedure as described for after the abundant occurrence of guards of the belemnite the Folkestone samples. The residues contained no hooks. Neohibolites minimus. The belemnite fauna from the O¨ lbach section has been studied by Spaeth (1971a, b). For Hannover-Lahe core this project a large quantity of claystone with abundant belemnite rostra was washed from a sampling point close Three hooks from a drill core at Hannover-Lahe, northwest to the bridge leading to the Schulte-Frankemo¨lle farm at Germany are considered for comparison. These are of the GPS coordinates 52°03027.100N, 006°57016.900E (collected same geological age as the Folkestone specimens. Locality by J.L. in February 2008). This site produced fresh details and a drawing of the section were given by 123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 291

Fig. 3 Position of samples in the Copt Point section, Folkestone, Kent (southern England) with stable oxygen isotope data following Kanungo (2005). The warming event in bed VIII coincides with a higher abundance of belemnite rostra and hooks obtained from microsamples 3 and 4. Profile sketch modified after field notes by H.G. Owen and added with own data. Bed numbers after Price (1874). Belemnite rostrum and hook indicate abundant occurrence at Folkestone, whereas range bars of belemnite species are an estimate following Spaeth (1973) given for the Ashford section, Kent (a Middle Albian occurrence of N. oxycaudatus at Folkestone is assumed following Keller et al. 1989, p. 279). N. oxycaudatus and N. ernsti are probably endemic to northwest Europe, whereas N. minimus is known from many areas in the Tethys (Mutterlose et al. 1983)

Table 1 Dry weight of samples and number of belemnite hooks obtained Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6

Dry weight (g) 2,201.9 2,066.0 3,778.4 3,909.9 3,643.0 3,836.8 Hooks in [63 lm fraction 13 12 40 37 22 25 Hooks in [125 lm fraction 413443 Hooks in [250 lm fraction –––––– Total number of hooks 17 13 43 41 26 28 Normalised to 500 g of sample 3.9 3.1 5.7 5.2 3.6 3.6

Lehmann et al. (2007). Recent revision of the biostratigraphy Germany. This applies to the material from the Copt Point of this site suggests that the critical core interval in between section, East Cliff, at Folkestone. The material from the 67.45 and 86.90 m depth is not Middle Albian, as interpreted Hannover-Lahe borehole (abbreviation ‘BGR’) is stored in by Lehmann et al. (2007), but corresponds in fact to the ear- the Bundesanstalt fu¨r Geowissenschaften und Rohstoffe liest Late Albian (early part of the Dipoloceras cristatum (Federal Institute for Geosciences and Natural Resources), ammonite Subzone; see also Erbacher et al. in press). Hannover, Germany.

Repository Systematic palaeontology

The abbreviation ‘GSUB’ indicates the repository in the The ﬁrst belemnoid arm hooks encountered in the 19th Geosciences Collection of the University of Bremen, century were meso- and macrofossils. Quenstedt (1858) 123 292 J. Lehmann et al.

encountered isolated larger hooks in the Jurassic of Swabia one per individual, and they are much larger than the other and termed these ‘‘Onychiten’’. He thereby introduced the arm hooks of the individual belemnite (Klug et al. 2009). parataxon Onychites that became extensively used later Kulicki and Szaniawski (1972) used the term ‘‘onychites’’ (e.g. Riedel 1938; Kulicki and Szaniawski 1972; as synonymous with only the smaller belemnite hooks, thus Schweigert 1999). These larger hooks are arranged in pairs, some subsequent authors have differentiated between

123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 293 b Plate 1 SEM images of belemnite hooks. 1 Arites sp.: 1a lateral view, Description of hooks 1b oblique lateral view, 1c detail of the transition between base and shaft, 1d base and lowermost part of the shaft in oblique lateral view, 1e part of the supraopening area with basal opening, 1f detail of uncinus with striae; The majority of hooks originate from the 63–125 lmsize GSUB C5639 (from sample 3 in Fig. 3). 2 Arites sp.: 2a lateral view, 2b fraction. Complete, undamaged hooks are confined to this detail of uncinus with striae, 2c detail of the inner part of the base and fraction (Plate 1, Figs. 1, 2, 5a–c). Hooks are generally mor- lowermost tip of the shaft; GSUB C5640 (from sample 4 in Fig. 3). 3 phologically very variable, but two general types can be dis- Hughowenites incurvatus n. gen. n. sp. (holotype): 3a lateral view, 3b close-up of the uncinus, 3c surface detail of the inner margin at the bend tinguished: Most hooks show a bow-like outline and are between the shaft and the uncinus; BGR 13804 (from 86.85–86.90 m typically hook-shaped (e.g. Fig. 5a, b). A second type is more depth). 4 Arites sp.: lateral view; BGR 104796 (from 67.45–67.65 m elongated and saber-like (Fig. 5e–g, m). After Klug et al. depth). 5 Hughowenites incurvatus n. gen. n. sp. (paratype): 5a detail of (2009) the former type is referred to the distal (tip) or middle outer margin in lateral view, 5b detail of the inner margin, showing the inner main ridges, oblique lateral view; BGR 13867 (from part of the belemnoid arm and the latter to the proximal part. 70.32–70.37 m). 1, 2 Earliest Late Albian, Dipoloceras cristatum The specific hook-like morphology of the first type can ammonite Subzone, Folkestone; from the [63 lm size fraction. 3–5 be referred to the paragenus Arites Kozur, 1967 as defined Same stratigraphic interval, Hannover-Lahe borehole, northern Germany; below. The elongated type of hooks shows a variety of for comparison with the hooks from Folkestone; see Lehmann et al. (2007) for details simple, non-characteristic shapes. Since we do not possess specimens preserved perfectly including the bases, they are mega-onychites and micro-onychites (Engeser 1987; not assigned to a parataxon. Engeser 1988; Fuchs 2006). Among the smaller hooks, a Belemnoidea Steinmann, 1890 number of parataxonomic genera have been established, as Uncinifera Engeser, 1990 summarised by Schlegelmilch (1998); among these, Belemnite hooks (micro-onychites sensu Engeser and Paraglycerites is the most characteristic type because of its Suthhof 1992) lateral appendage (e.g. Riegraf 1996; Schweigert 1999). Paragenus Arites Kozur 1967 For a recent and full discussion of belemnoid hook types and their distinction from allied forms see Fuchs (2006). Type species Arites vulgaris Kozur 1967 We agree with Engeser (1987) that it makes sense to use a parataxonomy for isolated hooks, and we apply a par- Diagnosis Hooks with a moderate to strong bend and a ataxonomy wherever possible for our material. However, to large uncinus. The base is usually slightly shorter than the avoid the confusion that exists through different definitions maximum length. The angle between the shaft inclination of the term ‘‘onychite’’, we use the neutral term ‘‘hooks’’ and the baseline lies between 30° and 70°. The surface is for the material discussed in this paper, contrary to the smooth; very faint lateral striae occur in some specimens. usage of Engeser (1987) and others. The inner margin occasionally bears distinct main ridges

Fig. 4 Terminology of features and measures of belemnite hooks used in the text. Note that inner main ridges visible in the oblique lateral view (b) are not visible in the lateral view (a). Stippled lines in (c) and (d) indicate angle measurements, dashed lines are length and height dimensions

123 294 J. Lehmann et al.

Fig. 5 Outlines of belemnite hooks from the Albian of Folkestone. Hooks ﬁgured in a–c are perfectly preserved and referable to the parataxon Arites sp., all others show damage and fractures and are not determined. d, e, g, k, l, n, t, u (GSUB C5641-C5648): sample 1; m, w (GSUB C5649- C5651): sample 2; a, b, f, i, o, r, v (GSUB C5652-C5658): sample 3; c, h, j, q, s (GSUB C5639, C5659-C5662): sample 4; p (GSUB C5663): sample 5. Position of samples see Fig. 3

(‘‘La¨ngsru¨cken’’ of Engeser and Suthhof 1992). The ele- preserved for any measurements. Estimating the position of ments lack a spur at the base of the inner margin. The base is the uncini in relation to the baseline in the fragmentary almost flat in lateral view. specimen indicates that the angles must have been much larger than in the few specimens where measurements are Remarks See Engeser and Suthhof (1992) for a distinc- possible. This is particularly true in some of the specimens tion of Arites from similar parataxa and a discussion of representing larger hooks (e.g. Fig. 5o–s). Therefore, Arites their affiliation. is probably highly variable. Morphologies comprise that of the type species Arites Arites sp. (Fig. 5a–d; Plate 1, Figs. 1, 2, 4) vulgaris Kozur 1967 as well as that of Arites keuperianus Kozur 1967 (both from the Triassic) and include features Description Complete hooks of this type have maximum seen in Arites riedeli Engeser & Suthhof 1992 from the length of about 400 lm, maximum breadth of 100 lm and Early Cretaceous. Since the two Triassic species are doc- maximum height of 190 lm (Fig. 4c for definition). The umented only by light-microscopic photographs, it was not curvature of this hook type is very variable, from wide possible to properly compare the described taxa. Therefore, (Fig. 5a and Plate 1, Fig. 2) to strongly incurved, tending it makes no sense to assign the present material to a species to develop a U-shaped outline (Fig. 5b; Plate 1, Fig. 2). or to establish a new species on the basis of morphology. The angle between shaft inclination and the baseline varies Furthermore, the full range of variability cannot be estab- largely in between 40° and 80°, whereas the angle between lished from the present material, and it would be poor uncinus and the baseline varies only little between 0° and taxonomic practice to establish a new parataxon solely on 6°. The central part of the inner margin bears a main ridge the basis of different stratigraphic occurrence. on each side of the specimen, thus the hook shows two A large part of the material is indeterminable at para- edges in cross-section rather than being well rounded. Shaft generic level since it is too fragmentary. A part of it and uncinus can be covered by faint lateral striae (Plate 1, probably represents Arites (e.g. Fig. 5j, t). Specimens in Figs. 1a, 2b). The base of the hook is covered by wrinkles Fig. 5v, w are examples of very widely curved hooks that (Plate 1, Fig. 1c, d; light grey area in Fig. 5). The supra- might be referrable to Falcunus Kulicki and Szaniawski opening area is widely concave, with a basal opening that 1972, a genus similar to Arites but that is described as is located in the middle of the base and is surrounded by a possessing a spur (Kulicki and Szaniawski 1972). shallow crest. Figure 5f, m shows sabre-blade-shaped hooks that are Remarks Most of the fragmentary material at hand missing their bases. They resemble species of Urbane- probably belongs to this paragenus, but it is too poorly kuncus Kulicki & Szaniawski 1972 but do not possess the 123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 295 characteristic short spur high above the base (Kulicki and These strong ridges clearly differ from the weak striae of Szaniawski 1972). Some authors interpret the occurrence all British specimens of the same geological age that are of spurs in belemnite hooks as indicative for guard-bearing referred herein to Arites sp. (compare Plate 1, Figs. 1, 2). belemnites (e.g. Riegraf and Hauff 1983; Engeser 1987; Occurrence See locus typicus and stratum typicum, spe- Riegraf 1996). This hypothesis is based only on specimens cies description below. of Passaloteuthis with in situ hooks, and contradictory ideas about the presence of spurs in this genus might Hughowenites incurvatus n. gen. n. sp. (Plate 1, indicate preparatorial or preservational artefacts. Thus Figs. 3, 5) spurs might also occur in belemnoteuthids and diplobelids and are possibly a feature typical at only the species level Derivatio nominis After Latin incurvatus, curved inward. (Fuchs 2006). Holotype BGR 13804; Plate 1, Fig. 3 Comparison with new material Paratype BGR 13867; Plate 1, Fig. 5 Lehmann et al. (2007) mentioned the occurrence of a Locus typicus Hannover-Lahe drilling core (holotype: couple of belemnite hooks from a drill core from Northern 86.85–86,90 m depth, paratype: 70.32–70.37 m depth; Germany. This material was discovered because the com- Lehmann et al. 2007) paratively large specimens attracted attention during stan- Stratum typicum Earliest Late Albian, Dipoloceras dard micropalaeontological screening. Since these cristatum ammonite Subzone belemnite hooks are the only other specimens known from Albian sediments they are compared with the Folkestone Description Large hook with maximum length of the shaft material. of [800 lm and a large uncinus with total length of about The specimens from northern Germany (Plate 1, Figs. 3, 600 lm. The shaft is of constant breadth of about 200 lm for 4, 5) agree in their bow-like outline with the majority of most of its length, except for the basalmost part of the inner hooks from Folkestone, but are fairly large compared with margin that is curved about 45° inwards. The shaft shows a the British specimens, of which only two fragments slight depression in the centre of the basal part that is (Fig. 5u, v) may have reached a similar size. Their large regarded as a primary feature. The largest part of the uncinus size might indicate that they belong to a larger animal or is strongly tapering; it is ornamented by pronounced ridges, that they originate from the middle part of a belemnite arm. about 20 on each side. The tip of the uncinus is smooth, The hook illustrated on Plate 1, Fig. 4 is attributed to strongly bent and inwardly recurved, thus it points towards Arites sp., but that on Plate 1, Fig. 3 differs from all other the middle part of the shaft (Plate 1, Fig. 3a). On the inner material of Arites and therefore is described as a new margin, there are very thin and distinct main ridges. parataxon below. Comparison As for genus. Paragenus Hughowenites n. gen. Discussion Type species Hughowenites incurvatus n. gen. n. sp. Derivatio nominis After Hugh G. Owen, London, out- Preservation potential standing geoscientist, who has worked on the Albian of Europe for many decades. Due to their massive nature, belemnite rostra are among the most abundant invertebrate fossils found in Jurassic and Diagnosis Large uncinus strongly recurved inwards; with Cretaceous marine sediments (e.g. Boardman et al. 1987). ultimate tip of the uncinus showing an extreme flexion, Despite the large quantities, however, they are not abun- pointing towards the middle of the shaft (Plate 1, Fig. 3a). dant enough to yield significant numbers throughout a Strongly pronounced ridges on the uncinus, except for the sedimentary succession—except through accumulation due smooth recurved tip. Very thin and distinct main ridges on to condensation, storms or currents (e.g. Mitchell 1992; the inner margin. Doyle and MacDonald 1993). Furthermore, there are sev- Comparison Hughowenites differs from all other belem- eral groups within the Belemnoidea that either lack a nite hooks in the extreme flexion of the ultimate tip of the guard, like the Phragmoteuthida, or have strongly reduced uncinus which points towards the middle of the shaft, as guards like the Diplobelida (Fuchs 2006). represented in the holotype. Furthermore, pronounced rid- This limits the application of belemnite guards as pal- ges on the uncinus are characteristic (Plate 1, Figs. 3, 5). aeoceanographic proxies and suggests value in studying

123 296 J. Lehmann et al. their hooks, which potentially should be abundant and very strongly curved hook and a series of lateral teeth. occur across the whole belemnite fauna. Occasionally, Scolecodonts can be additionally separated by their larger belemnite hooks have been found in microsamples brownish colour from belemnite hooks that are blackish. from claystones or by collecting macrofossils (Riedel 1936, Arites sp. described above is among the parataxa refer- 1938; Lehmann et al. 2007). Very few studies have suc- red to scolecodonts in the past (Kozur 1967; Kozur 1970; cessfully focussed on onychites (e.g. Engeser 1987; Kozur 1971), but good arguments for an assignment to Engeser and Clarke 1988; Engeser and Suthhof 1992). belemnoid coleoids have been given by Engeser and Belemnites preserved with hooklets and soft parts in situ Suthhof (1992). are known from not more than a couple of famous sites, such as the Early Toarcian Posidonia Shale in southwest Assignment of belemnite hooks Germany (Reitner and Urlichs 1983; Riegraf and Hauff 1983) and the Late Kimmeridgian Nusplingen Plattenkalk Although first reports of the common belemnites from (Schweigert 1999; Klug et al. 2009). This shows that Folkestone were published long ago, including the mono- preservation of more than the rostra needs exceptional graph of Swinnerton (1955), neither detailed range charts taphonomic conditions and is almost exclusively restricted nor an estimate of their quantitative distribution have been to conservation Fossillagersta¨tten (sensu Seilacher et al. given. This is probably due to mostly loose specimens 1985). having been collected. Most rostra belong to the Middle- Despite the abundance of Neohibolites rostra at both Late Albian Neohibolites minimus (Miller ex Lister, 1826), sampling sites, only Folkestone yielded hooks. This sur- a species comprising several subspecies. In addition, prising observation may be explained either by Neohibo- Neohibolites oxycaudatus Spaeth 1971a, b and Neohibo- lites being the only belemnoid occurring at the O¨ lbach lites ernsti Spaeth 1971a, b are early to middle Late Albian stream cut and that it did not possess hooks, or by pre- offshoots of N. minimus; all three are recorded from Ash- servational differences. The pure claystone facies of the ford, Kent, close to Folkestone (Spaeth 1973; Fig. 1). Gault Formation at Folkestone has allowed the preserva- According to our field observations, well-preserved guards tion of organic hard parts, such as belemnite hooks, with of Neohibolites spp. occur most frequently in the lower part high preservation potential indicated by the abundance of of bed VIII, corresponding to microsample 3 and therefore iridescent, aragonitic shells (e.g. Clouter 2007). In contrast, also to the sample with the highest hook abundance index the marly greensand of the O¨ lbach locality probably pro- (Fig. 3). This might indicate that the belemnite hooks vides poorer preservation potential with hooks having been belong to this genus. However, comparison of the present lost through taphonomy or diagenesis. hooks with those that are preserved in situ on the closest relative of Neohibolites shows distinct differences. Klug Distinction of belemnite hooks from scolecodonts et al. (2009) recently described a fossil that they attribute to Hibolites, a member of the same belemnite family—the Scolecodonts are fossil jaws of annelid worms (e.g. Kozur Belemnopseidae. Hooks of this fossil show some variation, 1970), often possessing a row of denticles, and they are but all hooks differ from Arites by showing a much smaller clearly different from belemnite hooks including those uncinus compared with the shaft. Furthermore, the mor- bearing a single spur on the basal inner margin. Never- phology of Arites, with a large uncinus compared with the theless, both are superficially similar, and scolecodonts shaft, is different from that of the hooks known from the have occasionally been mistaken as belemnite hooks few in situ finds of the massive guard-bearing belemnite (Engeser and Clarke 1988; Engeser and Suthhof 1992; order Belemnitida Zittel, 1895 (e.g. Riegraf and Hauff Riegraf 1995). In the case of fragmentary material, a 1983; Schlegelmilch 1998; Klug et al. 2009). These spec- large number of specimens usually permits unequivocal imens all bear hooks with a long shaft compared with the identification. uncinus and with the uncinus not being strongly bent as in Among the present material, each microsample contains Arites. This argues against an assignment of our hooks to one to six scolecodont specimens. These resemble belem- Neohibolites. nite hooks in their dark colour and preservation. Among Arites has been attributed by Engeser and Suthhof these, slender scolecodonts of curved conical shape are (1992) to belemnoid cephalopods, ‘‘possibly squids similar recorded and referred to as cf. Glycera sp., an extant genus to Phragmoteuthis’’ (translated from German). This is that has been recorded from the Cretaceous by Charletta based on the observation that similar hooks as in Arites and Boyer (1974) and Reich and Frenzel (1997). These can occur in Phragmoteuthis? ticinensis described by Rieber be easily distinguished from belemnite hooks since they (1970), a coleoid that is questionably referred to the show two canals, the pulp and poison cavity, in cross- phragmoteuthids, and in the alleged diplobelid Chondro- section. Another scolecodont type is very massive, with a teuthis. Diplobelina are always a subordinate part of the 123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 297 fossil fauna, known from only a few genera from Europe, and Owen (2010) assumed a temperature control on the the Lebanon and Mozambique (Mutterlose 1984). At occurrence of Neohibolites minimus in the Middle Albian Folkestone: two genera of the belemnite suborder Dip- Hoplites spathi Subzone because the species is relatively lobelina have been described: Conoteuthis woodwardi uncommon south of Bedfordshire and East Anglia, but Spath 1939 and Pavloviteuthis cantiana (Spath 1939) more abundant to the north. This observation appears (Spath 1939; compare ‘Locality details and methods’ contradictory to all previous results mentioned above, above). These single records do not allow estimation of however this has not been discussed by these authors. peak abundances within the Gault succession but clearly There are palaeotemperature estimates for the Albian show the presence of Diplobelina. based on a few Neohibolites rostra. Price (1998) calculated Engeser (1987) recorded arm hooks of Chondroteuthis mean water palaeotemperatures of 15.9–16.8°C from the wunnenbergi from the Early Toarcian of Gomaringen near oxygen isotope composition of Neohibolites rostra from the Tu¨bingen in southern Germany, which show wide variation Albian claystones at Speeton and Ferriby in northeast and lack a spur, but that also include very similar mor- England. These values are in accordance with those derived phologies to the material from Folkestone. Isolated hooks from circulation models (Barron et al. 1995) but are lower of Arites-like morphology have been recorded from the than sea-surface temperature estimates based on well-pre- Early Triassic (Kozur 1967,1970, 1971; Saslavskaja 1989), served Late Albian foraminifera (24–30°C for the northern the Late Jurassic (Kulicki and Szaniawski 1972) and the mid latitudes, Wilson and Norris 2001; Erbacher et al. in

Early (Engeser and Suthhof 1992) to Late Cretaceous press) or the TEX86 proxy (33°C for the tropical Atlantic, (Reich and Frenzel 2002). This supports Fuchs et al.’s Forster et al. 2007). Unfortunately oxygen isotope data (2004) inference that co-occurrence of typically curved derived from coccolith matrix as well as from benthic and hooks and diplobelid belemnoids in many intervals of the planktic foraminifera from the very same samples as those Mesozoic might indicate an origin of diplobelids as early as yielding Neohibolites at Speeton and Ferriby exhibit a the Triassic. Thus Arites in the Albian of Folkestone might diagenetic overprint (Price 1998). Therefore, the tempera- represent the hooks of the two diplobelids Conoteuthis tures estimated from Neohibolites cannot be compared with woodwardi and Pavloviteuthis cantiana rather than those from other groups of fossils. These generalised data belonging to the predominant guard-bearing Neohibolites. indicate a gap in our knowledge because there is a lack of Nevertheless, it is possible that the paragenus Arites is geochemical data documenting temperature fluctuations paraphyletic and this hook morphology might have devel- throughout a section from which quantitative belemnite oped separately in several belemnite lineages since the occurrences can be obtained. Triassic. Hooks as proxies for belemnite productivity? Climate preference indicated by belemnite shells Since belemnite hooks are generally rare, the possibility of Among the Albian belemnite fauna of Folkestone, the testing the usage of belemnite hooks as a proxy is limited diplobelid records are much too rare to permit any dis- currently to just a few sites. Nevertheless, under advanta- cussion in terms of possible climatic preferences, but there geous taphonomic conditions their preservation is not a are enough data for Neohibolites (Belemnitina). The bel- lucky strike but may be routine. Hooks occur much more emnite genus Neohibolites is believed to be of Tethyan frequently than rostra in a lithofacies that preserves both origin (Stevens 1965; Doyle 1988). Aptian representatives organic and calcareous hard parts, and they are present also are described as having had wide temperature tolerance and in guard-lacking belemnoids. Therefore, hooks are a being able to migrate from the Tethys into the Boreal realm potential proxy for higher belemnite productivity. Their during times of warm-water conditions (Mutterlose 1987, poorly known morphological range is more problematic, as 1988). In the Boreal realm the palaeogeographic and gen- too is the relationship between different hook types and eral stratigraphic distribution of Neohibolites reveals a species. This can only be improved by classifying a larger correspondence of increased abundance with warmer number of hook associations. Less significant is the fact intervals. An interpretation of Neohibolites as eurythermal that hooks might get concentrated, like belemnite guards, (Mutterlose et al. 1983) is in accordance with its distribu- in the stomach of larger vertebrates (Bo¨ttcher 1989). tion pattern ranging across climatic zones in the Aptian and Preservation of such accumulations seems inherently less Albian (Doyle 1987b), which indicates fairly high tem- likely than accumulation of rostra. Any preferential sorting perature tolerance. On the other hand, Mitchell (2005) of different hook types also seems unlikely for most provides little evidence for temperature control on the occurrences. Under favourable conditions for preservation distribution of Cenomanian belemnites based on d18O data of hooks, one needs distinctly less rock material to obtain obtained from Neohibolites among others. Recently, Gale quantitative data. Nevertheless, our sampling is too limited 123 298 J. Lehmann et al. and the total number of specimens per sample obtained is lithology remains similar throughout the section, enhancing too sparse to permit statistical study. Thus, before sug- the likelihood that diagenetic conditions were similar for gesting a new proxy for belemnite productivity (i.e. bel- the different levels of the succession; and (5) the occur- emnite abundance or standing stock), more studies from rence of a significant warming event across the Middle/ different stratigraphic levels and places are needed. Here, Late Albian boundary in northern Germany based on study we propose to test if belemnite hooks might be established of glassy-preserved foraminifera (Erbacher et al. in press). as a beneficial tool to better understand conservation Thus bed VIII at Folkestone can be assumed to have Fossillagersta¨tten. been deposited during a warming interval. This inferred warming corresponds to the observed increase in the hook The earliest Late Albian warming event abundance index as well as a higher abundance of rostra of Neohibolites (Fig. 3) and therefore might suggest a tem- During most of the Middle Albian, Tethyan macrofauna perature control on belemnite productivity. only sporadically invaded the Boreal shelf seas. This pat- The earliest Late Albian warming event in bed VIII is tern changed considerably in the Late Albian (Owen 1996; also accompanied by an increase in palaeoproductivity as Lehmann et al. 2007). A number of ammonites of Tethyan indicated by changing calcareous nannoplankton assem- origin appear for the first time in the Folkestone section blages. Kanungo (2005) records increased abundances of in bed VIII, namely Hypophylloceras subalpinum, Beu- Zeugrhabdotus noeliae of up to 40%. This is interpreted as danticeras beudanti, B. subparandieri, Neophlycticeras reflecting surface waters rich in nutrients (following e.g. (Eotropidoites) jayeti, Protissotia itierianum, Oxytropidoc- Erba 1992), because the warming event may have forced eras cantianum, Dipoloceras spp., Mortoniceras rigidum, higher precipitation rates leading to higher nutrient input Hysteroceras orbignyi, H. capricornu, H. pseudocornu- through run-off into the basin. Biscutum constans is a tum, H. symmetricum, H. simplicicosta and H. serpentinum second high-nutrient-index taxon that shows its peak (Casey 1966). Bed VIII represents the lower part of the occurrence in the lower part of bed VIII (22%). A third Dipoloceras cristatum ammonite Subzone, thus the base of high nutrient index is that of Discorhabdus ignotus, bed VIII corresponds with the base of the Late Albian showing a minor peak in bed VIII only (2%). Based on (Fig. 3). Besides the Tethyan ammonites, including the these indicators for eutrophic conditions, Kanungo (2005) most important group of mortoniceratids, a few Arctic calculated an index to estimate the palaeoproductivity for elements also occur for the first time (Owen 1973), and the Gault Clay. There is a trend to higher primary pro- thus, Owen (1996) assumed tectonic rather than primarily ductivity in bed VIII, with a peak in the upper part of climatic factors as underlying this invasion. Although the bed VIII. Thus, there are good arguments for higher Dipoloceras cristatum Subzone was clearly a time of nutrient levels coinciding with the warming event. considerable and widespread tectonic activity in Europe Higher primary productivity is likely to have had a (Owen 1971a; Owen 1973), new geochemical data support positive impact on organisms at higher trophic levels the idea that this faunal change was above all climatically within the food web. Thus, we argue that the increased steered. The oxygen isotope data obtained from bulk rock occurrence of belemnite hooks in bed VIII and possibly samples at Folkestone (from the same spot as our samples, also the increased occurrence of rostra at the base of see Fig. 2) presented by Kanungo et al. (2004) and Kan- bed VIII might be due to both an increase in productivity ungo (2005) indicate an increase of palaeotemperature as well as warmer temperatures (Fig. 3). during bed VIII (Fig. 3). The palaeotemperature rise from the Middle to Late Albian was estimated to have been on Sea level changes and their possible consequences the order of about 5–6°C (Kanungo 2005, p. 80), but diagenetic overprinting in Albian claystones cannot be ruled Following the classical papers on sea level change by Haq out. Nevertheless, alteration of the absolute oxygen isotope et al. (1987) and Hardenbol et al. (1998) as well as suc- values is not important for the present study, as the trend of ceeding papers (e.g. Immenhauser and Scott 1999), the the isotope curve very likely represents a primary signal for Middle–Upper Albian boundary interval comprises a a number of reasons: (1) the excellent preservation and sequence boundary (Fig. 3). The earliest Late Albian high diversity of calcareous nannoplankton in the samples, therefore not only correlates with a short-term warming with even the more delicate coccolith rims being well event and increased palaeoproductivity, but also with a preserved (Kanungo 2005); (2) the warming indicated by third-order sea level rise. The greatest rise in sea level stable oxygen isotope data occurs synchronously with the probably took place during deposition of bed VIII, since shift to warm-water ammonite faunas; (3) a decline in the this bed contains several nodule layers that might indicate occurrence of the cold-water calcareous nannoplankton condensation. Formation of these nodule layers might have indicator Repagulum parvidentatum (Kanungo 2005); (4) been due to sediment starvation during rapid sea level rise 123 Belemnoid arm hooks from the Middle–Upper Albian boundary interval 299 at some distance from the shoreline (e.g. Sturrock 1996). 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